On an expedition early in his career, Michael Huffman was watching a group of chimpanzees in an East African jungle when the primate researcher made a surprising observation. A mother chimp lay ill on a bed of branches in a tree as her two-year-old son climbed dangerously high. Too sick to scold or bring down her offspring, she simply ignored him.

A while later, the female chimp summoned the energy to climb to the ground. She then slowly ambled over to a shrub. Huffman watched as she removed s...